Means for producing high temperature plasma



June 15, 1965 R. M. PATRICK 3,139,523

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R. M. PATRICK MEANS FOR PRODUCING HIGH TEMPERATURE PLASMA June 15, 1965 Filed March 27. 1961 ll 0 II II\ United States Patent 3,189,523 lVLEANS FOR PRODUCING HIGH TEMPERATURE PLASMA Richard M. Patrick, Winchester, Mass., assignor to Avco Corporation, Cincinnati, Ohio, a corporation of Ohio Filed Mar. 27, 1961, Ser. No. 98,539 8 Claims. (Cl. 176-6) The present invention relates to a device for producing extremely high temperature plasma. In operation, the device resembles a magnetic shock tube, particularly one in which electromagnetic forces are employed to establish a high velocity shock wave by rapid acceleration of an ionized plasma. A particularly novel feature of the in- 'vention is its arrangement whereby the shock wave is refiected from a magnetic barrier back into the plasma initially behind the shock wave. The reflected wave suddenly brings the plasma to rest causing its kinetic energy to be converted into thermal energy and its temperature to rise several hundred million degrees Kelvin. Not only is the invention useful in producing high temperature plasma but also in holding the plasma at such temperature for an extended time period.

The present invention is an improvement over the gas accelerator disclosed in presently pending application Serial No. 752,309, that was filed on July 31, 1958, by Dr. George Sargent lanes and Dr. Richard M. Patrick. The gas accelerator set forth in that application comprises an annulus defined in part by inner and outer concentric cylindrical electrodes. Between the electrodes and closing the annulus at one end thereof, is an electrical insulator making it possible to impose a large voltage difierence across the electrodes without short circuit. Also associated with the electrodes are cylindrical insulating walls that define an annular space forming an extension of the annulus between the electrodes. Surrounding the cylindrical insulating walls are electrically conductive nonmagnetic shields.

Around the exterior of the device is a coil for establishing an axial magnetic field through the annular space. The axial magnetic field, designated B interacts with the radial electric field between the electrodes. A gas, such as hydrogen gas, is introduced to the region of the electrodes and is initially ionized by electron movement circumferentially around the annulus between the electrodes under the influence of the electric field and the B magnetic field. After dissociation and ionization, the resulting plasma becomes sufiiciently conductive to convey an electric discharge between the electrodes. The current sheet formed thereby reacts with its own associated circumferential magnetic field, designated B The cross product thereof propels the current sheet, which remains in conductive relationship with the electrodes, along'th-e annulus away from the electrodes. The movement of the current sheet is so rapid that a shock wave forms ahead of it in the annulus. Behind the shock wave, plasma temperatures attain extremely high values.

During expansion of the current sheet, radial movement of the plasma towards the confining walls is opposed by image currents formed in the shields. The axial field B is compressed between the image currents and the plasma forming a magnetic barrier opposing radial expansion of the plasma. Another coil may be provided inside the inner shield to augment the B field in the annular space through which the plasma is driven. To further enhance operation, a current path may be provided centrally through the device. The circumferential magnetic bias field B, resulting from the current flowing in the central conductor, allows one to achieve a nearly perfect MHD shock wave and more particularly, higher shock velocities and higher energy densities than heretofore attainable. The device described to this point may be used to pro- 3,189,523 Patented June 15, 1965 pel gas at high velocity from the open end of the annulus. When used in this manner, the device is an excellent propulsion engine. The device may also be used to study high temperature gas properties but the plasma can be maintained at high temperature for only short durations. This is undesirable for some purposes where it would be helpful if the gas could be maintained at temperatures for a more extended period.

The present invention represents an improvement over the above described device in several important respects. .For one thing, an improved manner of pre-ionizing the gas between the electrodes has been found. Of even greater importance is the addition of a radial magnetic field, or a barrier field, designated B transversely of the annular space remote from the electrodes. As the shock wave, moving along the annulus at high velocity, encounters the barrier field, it undergoes a substantially instantaneous reflection or reversal of direction such that the plasma that was initially behind the incident shock wave is suddenly brought to rest. As a result, the kinetic energy of the plasma is suddenly converted into thermal energy increasing the plasma temperature markedly. Not only can large temperature increases be realized, but the time during which the plasma may be held at such temperatures may also be prolonged for as long as 10 microseconds. Indeed', by use of the present device, it is anticipated that the time duration can be increased to pcriods of several milliseconds.

The importance of the invention to those studying transport properties of gases can hardly be overestimated since gas under study can be held at high temperatures for a relatively long time. Such transport properties normally include thermal conductivity, electrical conductivity, and the mass diffusion characteristics of the gas.

In view of the foregoing, it will be understood that an important object of the invention is to provide a device capable of producing a nearly perfect MHD shock wave and more particularly, higher shock velocities and higher energy densities than can be attained by prior art devices which depend upon particle collision.

Another important object of the invention is to provide a device for instantaneously reflecting a shock wave whereby an associated mass of plasma can suddenly be brought to rest and held at high temperature for prolonged periods.

Another object of the invention is to provide a novel combination of elements in which the Alfven velocity of a plasma is increased by the provision of a magnetic field through the plasma in association with means for arresting the plasma by means of a shock wave reflected from a magnetic field transverse of the direction of movement of the plasma.

Other objects of the invention are to provide:

(a) A device capable of producing plasmas of extremely high temperature.

(b) A device capable of producing and maintaining plasma at high temperatures for extending time periods.

(c) A device capable of producing high temperature plasma free of contaminants.

(d) A device for producing nearly planar, extremely high velocity MHD shock waves.

(e) A device capable of producing a very high speed shock wave where the particle energies are sufficiently high so that collisions do not govern the shock structure.

The novel features that are considered characteristic of the invention are set forth in the appended claims; the invention itself, however, both as to its organization and method of operation, together with additional objects and advantages thereof, will best be understood from the following description of a specific embodiment when read in conjunction with the accompanying drawings, in which FIGURE 1 is a longitudinal sectional view through '3 the novel device showing the details of its interior construction; and

FIGURE 2 is a diagrammatic view of the device showing the various magnetic fields and their influence on plasma movement within the device.

As used in this specification, the term plasma denotes an electrically neutral mixture of electrons, positive ions and neutral atoms. Although the gas ionized within the novel device described herein is not regarded as critical, it has been found convenient to use hydrogen because its simple atomic structure permits complete ionization at relatively low energies per particle.

Directing attention now to FIGURE 1, it will be noted that the device includes an inner cylindrical electrically conductive electrode 1 concentrically positioned within an outer electrode 2. Electrode 1 may be made integrally with an end cap 3 which includes a threaded extension 4 to which electrical connection may be made as will be explained. The electrodes are electrically isolated from one another by a cylindrical insulator 5 which may be secured to a supporting framework (not shown), and may be electrically isolated from the two conducting cylinders that form the annulus. The inner electrode may be secured to the insulator 5 by means of a plurality of cap screws such as indicated at 6. The outer electrode 2 may also be secured to the insulator 5 by means of a conducting ring 7 which is brazed to the electrode and secured to the insulator by bolts 8. Electrical connection is made to the outer electrode through the ring 7 as will be explained shortly.

Disposed within the inner electrode is a cylindrical inner wall 9 made from electrically conductive nonmagnetic material such as stainless steel. An outer cylindrical wall 10 of the same material, surrounds the outside of electrode 2. These walls, in cooperation with the electrodes, define between them an annulus 11 into which gas may be introduced as will now be explained.

For introducing the gas, a pipe 12 is secured to ring 7. Communication is established from the pipe through passageway 13 in the ring to an annular groove 14 formed in the exterior of the insulator 5. The groove is turn communicates with a tapered flow channel 15 defined by the external tapered wall 16 of the insulator 5 and the interior cylindrical wall of the elecrode 2. Thus, gas introduced through pipe 12, may flow, via passageway 13, groove 14, and the tapered channel 15 to the annulus 11.

Attention is directed :to the right hand end, as viewed in FIGURE 1, of the annulus 11. It will be noted that it is closed by a cover plate 17 which spans the distance across the annulus and engages the inner wall 9. The cover plate is secured to a flange 18 which may be secured to cylinder 19 at the other end of which is a flange 20. Flange 20 is secured to ring 21 which surrounds the exterior of outer wall 10 in sealing engagement therewith. The flanges and cover plates are supported by studs 22 from a fixed support ring 23, about which more will be said later.

Since the annulus must be sealed against leakage, a plurality of O ring seals are provided between the various components at positions where gas leakage might occur. Thus, an O ring 25 is provided between cap 3 of the inner electrode and the adjacent face of insulator 5 as illustrated. To provide an effective seal, discs 26 and 27 are provided inside of the inner Wall 9 and are held securely in place by electrical connector 28 which passes centrally through the discs and is engaged by nut 29. Associated with the discs 26 and 27 and cover plate 17, as well as flanges 18 and 20 and ring 21 are additional 0 ring seals. Other 0 ring seals are provided as illustrated in FIGURE 1 to prevent leakage between mating parts. See, for instance, seal rings 30 and 31. A gland ring 32 of insulating material is also bolted to ring 7 to position seal 33 adjacent the exterior of wall 10.

From the foregoing it will be understood that the annulus 11 is carefully sealed so that it may be evacuated through connector 34 which may be connected to a conventional Vacuum pump (not shown).

concentrically positioned within inner Wall 9 is a conductor 35 that is attachted to electrical connector 28. The conductor 35 is electrically connected through terminal 36 and conducting cylinder 37 to conductive ring 38. The ring is secured to one end of a cylindrical conductor 39 having a flange 40. By applying a potential difference across connector 28 and flange 40, current can be made to flow through conductor 35.

The conductor is filled with a nonmagnetic, nonconducting material, such as wood or plastic 35a, in order to lend rigidity to the conductor and prevent distortion under the influence of electromagnetic forces resulting from operation of the device. Longitudinal slots 35b are provided in the conductor 35 to accommodate magnetic flux associated with the coaxial coil now to be described.

A coil form 41 of insulating material surrounds conductor 35 and is supported thereby. A continuous electrical coil 42 surrounds the coil form and aids in pro viding B flux lines through the annulus 11.

ciated with another coil 43 wound about coil form 44 which surrounds cylindrical conductor 39. From a structural standpoint, it is important to note that flange may be secured to a fixed insulator (not shown) which not only supports the conductor 39 but also the ring 38 and the associated coil form 44.

A shield of magnetic material 45 may be secured to form 41 to confine the B field to that region of the annulus to the right of electrodes 1 and 2 as illustrated in FIGURE 1.

It will be helpful at this point to study the structure at the left end of the generator. It will be noted that the connector 28 passes through an insulating sleeve 46. Nut 29, threadedly engaged with connector 28, facilitates electrical connection thereto as will be described.

The extension 4 of cap 3 is concentric with connector 28 and insulated therefrom by the insulating sleeve 46. Nut 47 facilitates electrical connection to the end cap. Thus, the concentric conductors permit electrical connection to conductor 35 and inner electrode 1.

Imbedded within the insulator 5 adjacent end 5a is a radially disposed spiral conductor 49. Conductors 50 and 51 are connected to the spiral and make series circuit with a switch 52 and a high frequency source of electrical energy 53, such as 10 megacycles at kv.

When the device is to be operated, the annulus 11 is first evacuated. A small amount of gas is then admitted through pipe 12 and flows, as has been explained, to the annulus between electrodes 1 and 2. Simultaneously, switch 52 is closed providing a high frequency field between the electrodes. The moving lines of force in the presense of a gas that is inherently slightly conductive produces circumferential or azimuthal circulation of current within the gas. The few electrons that are inherently present in the gas are thus carried around the annulus and impinge against the gas atoms, breaking them down and assuring ionization in the entire region between the electrodes.

Simultaneously, a large DC. potential difference is applied to the electrodes 1 and 2 by associated conductors 54 and 55, respectively, and switch 56. The conductors are connected via switch 56 to a highly charged capacitor bank 57. As soon as switch 56 is closed, a strong radial electric field is established between the electrodes 1 and 2. To promote electrical discharge through the ionized gas between the electrodes, annular spikes 1a and 2a are provided.

As current flows between the electrodes, a strong circurriferential or azimuthal field B is created between the electrodes. The azimuthal magnetic field interacts with the radial current discharge to propel the current sheet to the right along the annulus 11. As the current sheet The flux lines are reinforced within the annulus by the flux asso advances, it continues to produce its own B, field. The current sheet lies closely adjacent to or in the inner and outer walls 9 and 10. The walls are electrically conductive and no insulation is provided between the plasma and the conductive walls.

Radial movement of the plasma within the annulus and into contact with the walls 9 and may be retarded by the axial magnetic field B created by coils 42 and 43 which are energized by a conventional D.C. source (not shown). Such radial movement of the plasma as occurs sets up image currents in the walls 9 and 10. The B field is compressed between the current loops formed in the inner and outer walls and the plasma, forming a. buffer and hindering the plasma from coming into contact with the walls and being cooled thereby. In addition, the interface between the driving currents and the shock heated plasma may be stabilized by the addition of the Bx field.

As the plasma is driven along the annulus by the advancing current sheet, a very high velocity is attained and a shock wave forms in the plasma. Behind the shock wave plasma temperatures attain very high values. The velocity that the shock wave may attain is proportional to the Alfven velocity and the speed of sound in the plasma medium. It is well known that a disturbance will propagate as a shock wave in a given medium if its velocity exceeds 0, where c is the velocity of a small disturbance ahead of the shock. In this case:

1 V Alfven velo city 'y=r-atio of specific heat at constant pressure to constant volume p=pressure p=density B =magnitude of magnetic field in advance of shock wave n =4r1r 10- henries/meter=permeability of free space a =veloeity of sound in medium In order to increase the value of c and hence the initial shock wave velocity, an azimuthal magnetic bias field B, is provided in annulus I111. The B, field is produced by DC. current from source 58 which flows through conductor 35 via conductors 59, 60 when switch 61 is closed simultaneously with the closing of switches 52 and 56. The resulting B, field provided in this manner conditions the plasma, or establishes an environment within the plasma, making possible extremely high shock velocities. Further, it is important to note that the shock wave is produced, not by particle collisions, as in chemical shock tubes, but by. electromagnetic eifects. 2 3 The result is that higher shock velocities and higher energy densities can be attained than possible using any known prior art device.

As the shock wave advances toward the right of the annulus, it impinges against a radial barrier field B produced by coils 62 and 63 surrounding the exterior of coil form 44. The coils are oppositely polarized by a conventional D.C. source (not shown) so that their associated flux lines reinforce each other and provide a nearly radial distribution of flux across the annulus (see FIG- URE 2).

Author: Patrick, R. M., Production of Very High Speed Shock Waves, Physics of Fluids, vol. II, Nov.-Dec. 1959.

Authors: Kemp, N. H., and Petschek, H. E., Theory of the Flow in the Magnetic Annular Shock Wave, Physics of Fluids, vol. II. Nov.-Dec. 1959.

3 Authors Fishman, F. .T., Kantrowitz, A. R., and Petschek, H. E., Magnetohydrodynamic Shock Wave in a C0ll1s1on-Free Plasma, Reviews of Modern Physics, vol. 32, Oct. 1960.

Other means may be used to provide the barrier field. For instance, a single coil may be employed axially spaced from an annular magnetic shield for preventing fringing of the flux lines. Supplementary coils could also be provided inside the annulus, as shown by dash lines at 64 in FIGURE 1. Furthermore, a series of conducting loops may be inserted in the annulus at 65 to reinforce the B field when the shock arrives.

As the shock wave encounters the barrier field, the magnetic lines are compressed and repel the shock wave back towards the oncoming current sheet. The reflection occurs practically instantaneously. Upon impact of the reflected wave and the plasma, the plasma movement is suddenly arrested. As a result, the temperature of the plasma rapidly increases (approximately doubles) as does the pressure. The compressed, high temperature plasma remains relatively stationary within the annulus making possible a study of its transport properties as has been mentioned.

It will be noted that the onrushing current sheet can be brought abruptly to a standstill because it is massless, comprising a current discharge and its associated magnetic field. This is in contrast to chemical shock tubes in which the propelling force is a mass of combustion products the momentum of which causes them to overtake and disperse the plasma if the plasma is arrested in its movement.

Returning to a consideration of the present device, the compressed plasma will remain relatively stationary within the annulus subject only to dissipation of energy to the walls of the annulus and to decay of the current sheet. The decay time may be in the order of several microseconds if the electrodes remain connected in series with the capacitor bank 57. By choosing the capacitance of the bank so that the time constant of the circuit is relatively long, the decay time can be prolonged and, as a result, the compressed plasma may be held in a relatively fixed position within the annulus and at high temperature.

In order to prolong the decay time the capacitor bank 57 may be disconnected from the electrodes by opening switch 56 at the time of impingement of the reflected shock front and the oncoming plasma. The electrodes can then be short-circuited (known as crowbarring) by closing switch 58. The short-circuited electrodes, in conjunction with the current sheet, then constitute a series RL circuit, the decay time of which depends upon the conductivity of the current sheet within the device.

Eventually, the plasma cools by heat transfer to the walls of the annulus. This results both from radiation of heat and diffusion of plasma particles into conductive relationship with the walls. Movement of the plasma radially, however, is retarded significantly by the B field in conjunction with the current loops formed in the inner and outer walls, as has been explained.

In theory, the decay time of the current sheet can be prolonged still more if, instead of short-circuiting the electrodes after they are disconnected from the capacitor bank, they are connected to a generator that can continue to supply energy to the current sheet at a controlled rate. Such would be possible if a transmission line generator of appropriate characteristics were connected across the electrodes at the time of their disconnection from the capacitor bank. By proper sequencing of events, the connection of the transmission line generator to the electrodes could be made to coincide exactly with the impingement of the reflected shock front with the plasma. Under such conditions, the rise time of current at the time of the plasmashock wave impingement could be made practically instantaneous, resulting in still greater temperature increases.

Attention may now be directed to FIGURE 2 showing schematically the current sheet C proceeding to the right along the annulus 11. In advance of the current sheet is the shock Wave S behind which the plasma is highly heated. Note the presence of the B field tightly compressed 7 along the inner and outer walls 9 and 10 which define the annulus.

Shown in phantom lines is the shock wave S after reflection from the radial barrier field H The position of the current sheet at the time of impingement of the refiected shock wave and the onrushing plasma is designated by the phantom line C. 1

It will be noted that the impingement of the shock front occurs relatively remote from the electrodes. This is highly desirable in that the plasma is positioned for study relatively far from the electrodes and any contaminants that might have been formed at the electrodes as a result of the initial current discharge.

It is noteworthy that, due to its inherent mechanical and electrical symmetry, the present device is not only capable of producing a nearly perfect MHD shock wave but also one that is almost perfectly disposed within a radimlane as illustrated in FIGURE 2. This is particularly true of devices of the type illustrated if they are built on a relatively large scale where the radius of the inner wall to the outer wall approaches unity.

An understanding of the broad principles of the invention can be understood from the following mathematical analysis. Assuming that the voltage between the electrodes during the time that the current sheet exists is V, the following computation may be made.

d V= (IL) +IR (1) d1 dL f f R where:

=m l ge (3) L=inductance of annular gas space through which current discharges l=1ength from electrodes to radial current sheet 1=current flow in current sheet R=resistance of current sheet (substantially constant) r =inside radius of current sheet r =outside radius of current sheet It will be noted that the value of L is a function of l, the physical length from the electrodes to the radial current sheet at any point in time. At the moment of reflection from the barrier field, I no longer changes and the derivative dL I goes to zero. If continuity of the voltage-time relation-- ship is to exist, it is evident that the value of dI E in the expression (2) must rap-idly increase. As the value of falls to zero, the existence of that condition is transmitted with the speed of light along the current sheet back to the electrodes. It is only .that small delay that prevents the rise in I from being instantaneous. As a result, the how of current to the current sheet rapidly increases, increasing and maintaining the electromagnetic pressure on the plasma being driven towards the barrier field,

In an actual device of the type illustrated, the following parameters have been successfully used, but should not be regarded as limitations of the invention:

Annulus spacing 2.5 cm., i.e., 1".

Mean radius 15 cm., i.e., 6".

Total length cm., i.e., 5.

Gas Hydrogen or deuterium. Initial pressure 0.01 to 0.5 mm, Hg. Pres-sure behind shock 1'0 atmospheres.

Temperature behind shock 10 K, Rise time of driving currents 2-5 ,usec., i.e., 2-5 010 sec. Driving current 10 amperes. Voltage 20,000 to 40,000 volts. B, bias field 5,000 to 10,000 gauss. B field 700 to 2000 gauss. B field 10,000 to 40,000 gauss.

In addition to the value of the present device as a research tool, it is believed to be useful in producing gas of a temperature sufiicient to initiate a fusion type reaction.

The various features and advantages of the device are thought to be clear from the foregoing description. Other features and advantages not specifically enumerated, will undoubtedly occur to those versed in the art, as likewise will many variations and modifications of the preferred embodiment of the invention illustrated, all of which may be achieved without departing from the spirit and scope of the invention as defined by the following claims.

I claim:

1. Apparatus for producing .high temperature plasma comprising inner and outer concentric cylinders of electnically conductive nonmagnetic material defining an annular space therebetween, cylindrical electrodes extending into the space from one end thereof, insulating means between said electrodes and closing one end of the space, means for sealing the other end of the annular space, means for evacuating the space, a continuous electrical coil Within the inner cylinder and concentric therewith, a continuous electrical coil concentric with and surrounding said outer cylinder, said coils establishing a magnetic field longitudinally through the annular space, another coil surrounding said outer cylinder at its end remote from said electrodes for establishing a radially disposed magnetic barrier field transverse of the annular space, a gas source, means -for admitting gas from said source to the annular space adjacent said electrodes, a high frequency coil in said insulator for pre-ionizing the gas between said electrodes to produce plasma, and means for establishing a voltage differential between said electrodes, whereby current is discharged between said electrodes and through the plasma forming a radial current sheet, the current sheet establishing an azimuthal magnetic field that interacts with the current sheet to propel it through the annular space toward the barrier field thereby accelerating the plasma and forming a shock wave in advance of the plasma, the shock Wave, .upon impact with the barrier field, being reflected back toward the moving plasma and rapidly decelerating the plasma whereby its kinetic energy is converted to thermal energy.

2. In combination concentric cylinders defining an annular space, cylindrical electrodes extending into the space from one end thereof, insulating means between said electrodes closing one end of the space, a gas source, means for admitting gas from said source to the annular space adjacent said electrodes, a high frequency coil in said insulator for ionizing the gas between said electrodes to produce plasma, means for establishing a voltage diiTeren-tial between said electrodes whereby current is discharged between said electrodes and through the plasma forming a radial current sheet, the current sheet establishing an azimuthal magnetic field in the annular space inter-acting with the current sheet to propel it through .the annular space thereby accelerating the plasma and forming a shock wave in advance of the plasma, and coils adjacent the annular space for establishing a transverse magnetic bar- 9 rier field for reflecting the shock wave back into the moving plasma.

3. Apparatus as defined in claim 2 in which said cylinders are made of electrically conductive nonmagnetic material, and in which coils are provided for establishing a magnetic field through the annular space for retarding movement of the plasma towards said cylinders defining the annular space.

4. Apparatus as defined in claim 3 and, in addition, an electrical conductor extending longitudinally through the said cylinders, and means for discharging current through said conductor to establish an azimuthal magnetic field within the annular space.

5. A device for producing high temperature plasma comprising: concentric members defining an annulus, means for evacuating the annulus, a source of gas, means for introducing the gas to the annulus, high frequency electrical means for ionizing the gas in the annulus to form plasma, means for establishing an azimuthal magnetic bias field within the annulus, means for establishing a magnetic barrier field transverse of the annulus, and means for accelerating the plasma to initiate a shock wave within the annulus travelling toward the barrier field, the shock wave upon impingement with the barrier field being reflected therefrom to decelerate the plasma.

6. A device tor producing high temperature plasma and maintaining the plasma at high temperatures for extended periods comprising: concentric cylindrical walls defining an evacuated annulus, means for supplying plasma to one end of the annulus, means for accelerating the 10 plasma towards the other end of the annulus and establish- 'ing a shock wave in advance of the moving plasma, and means for establishing a magnetic Ibarrier field at said other end of the annulus transverse of the direction of plasma movement for reflecting the shock Wave back to- Ward the moving plasma.

7. Apparatus as defined in claim 6, and, in addition, means for establishing an azimuthal magnetic bias field within .the annulus, to increase the Aliven velocity of the plasma.

8. Apparatus as defined in claim 7 in which said cylindrical walls are electrically conductive and nonmagnetic, and, in addition, means for establishing a magnetic field along the length of the annulus to retard movement of the plasma toward said cylindrical walls.

References Cited by the Examiner UNITED STATES PATENTS 2,940,01 1 6/60 Kolb l76--7 3,005,931 10/61 Dandl 315111 3,016,341 1/ 62 SpitZer 176-9 3,031,398 4/62 Tuck 1762 3,074,875 l/ 63 Alfven 176-6 3,093,765 6/ 63 Prevot 176-5 FOREIGN PATENTS 846,547 8/60 Great Britain.

CARL D. QUARFORTH, Primary Examiner. REUBEN EPSTEIN, JOHN W. HUCKERT, Examiners.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,189,523

June 15, 1965 Richard M, Patrick It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2, line 57, for "extending" read extended column 3, line 42, for "is" read Signed and sealed this 21st day of December 1965.

( L) Attest:

ERNEST SWIDER Attesting O fficer EDWARD-J. BRENNER Commissioner of Patents 

1. APPARATUS FOR PRODUCING HIGH TEMPERATURE PLASMA COMPRISING INNER AND OUTER CONCENTRIC CYLINDERS OF ELECTRICALLY CONDUCTIVE NONMAGNETIC MATERIAL DEFINING AN ANNULAR SPACE THEREBETWEEN, CYLINDRICAL ELECTRODES EXTENDING INTO THE SPACE FROM ONE END THEREOF, INSULATING MEANS BETWEEN SAID ELECTRODES AND CLOSING ONE END OF THE SPACE, MEANS FOR SEALING THE OTHER END OF THE ANNULAR SPACE, MEANS FOR EVACUATING THE SPACE, A CONTINUOUS ELECTRICAL COIL WITHIN THE INNER CYLINDER AND CONCENTRIC THEREWITH, A CONTINUOUS ELECTRICAL COIL CONCENTRIC WITH AND SURROUNDING SAID OUTER CYLINDER, SAID COILS ESTABLISHING A MAGNETIC FIELD LONGITUDINALLY THROUGH THE ANNULAR SPACE, ANOTHER COIL SURROUNDING SAID OUTER CYLINDER AT ITS END REMOTE FROM SAID ELECTRODES FOR ESTABLISHING A RADIALLY DISPOSED MAGNETIC BARRIER FIELD TRANSVERSE OF THE ANNULAR SPACE, A GAS SOURCE, MEANS FOR ADMITTING GAS FROM SAID SOURCE TO THE ANNULAR SPACE ADJACENT SAID ELECTRODES, A HIGH FREQUENCY COIL IN SAID INSULATOR FOR PRE-IONIZING THE GAS BETWEEN SAID ELECTRODES TO PRODUCE PLASMA, AND MEANS FOR ESTABLISHING A VOLTAGE DIFFERENTIAL BETWEEN SAID ELECTRODES, WHEREBY CURRENT IS DISCHARGED BETWEEN SAID ELECTRODES AND THROUGH THE PLASMA FORMING A RADIAL CURRENT SHEET, THE CURRENT SHEET ESTABLISHING AN AZIMUTHAL MAGNETIC FIELD THAT INTERACTS WITH THE CURRENT SHEET TO PROPEL IT THROUGH THE ANNULAR SPACE TOWARD THE BARRIER FIELD THEREBY ACCELERATING THE PLASMA AND FORMING A SHOCK WAVE IN ADVANCE OF THE PLASMA, THE SHOCK WAVE, UPON IMPACT WITH THE BARRIER FIELD, BEING REFLECTED BACK TOWARD THE MOVING PLASMA AND RAPIDLY DECELERATING THE PLASMA WHEREBY ITS KENETIC ENERGY IS CONVERTED TO THERMAL ENERGY. 